One of the problems encountered in the design of pollution control apparatus is the lack of a standard means to predict accurately the gas cleaning efficiency of pollution control devices. For years, pollution control engineers have used particle size as the main criteria in their calculations for gas cleaning efficiency. This was particularly true for Venturi Scrubbers. However, particle size alone does not determine gas cleaning efficiency and using this measure alone is inadequate for practical design work.
The method of this invention accomplishes the above by introducing the new concepts of collectability and collectivity which take into account all of the variables and mechanisms involved in the wet collection process known as impaction. Heretofore, particle size and particle size distribution were the main criteria in design calculations. Particle size alone, however, does not determine gas cleaning efficiency and Venturi pressure drop. Other particle characteristics such as shape, density and electrostatic charge must be taken into consideration. A term called "aerodynamic particle diameter" takes into account shape and density but not electrostatic charge.
The present invention comprises a method and apparatus for accurately quantifying the collectivity of a mixture of dust particles with various collectabilities. Knowing the collectivity of the dust mixture in a dust laden air/gas stream as described in this invention, the following can be accomplished:
1. The collectability of the dust particles will be expressed as positive fractions between zero and one.
2. The collectivity of the dust mixture will be reported in a table or a graph showing weight fraction versus collectability.
3. By determining the collectivity of a dust from a dust generating process, the Venturi pressure drop required for any gas cleaning efficiency or outlet dust concentration can be determined without the necessity of making pilot plant studies.
4. By testing the inlet and the outlet gas streams of a pollution control system, its comparative performance will be known. Knowing the collectivity of the inlet and outlet gas streams, not only the system's actual efficiency on particles of all collectabilities can be calculated but these actual efficiencies can be compared to those efficiencies of all other systems tested in this manner even if the systems are on different applications. Thus, we have a means for comparing gas cleaning systems on boilers, blast furnaces, kilns, incinerators and all other applications.
5. Obviously, liquid entrainment can be determined by the gain of water in the first impinger if other gains/losses are taken into account. But more important, the amount of particulate matter in this liquid entrainment can be determined using the concept of collectability.
Specifically, there is no relevant prior art of record since applicant is disclosing a new concept herein. Consequently, the cited prior art is merely of marginal interest although the invention may lie in the same general field. In prior art, cascade impactors have been used to determine particle size but the present invention relates to collectability as defined herein.
In the prior art, Davis et al U.S. Pat. No. 4,509,727 discloses an off-gas monitor for determining gas scrubber efficiency in steel processes. The method comprises comparing the particulate matter in a gas stream before and after chemical treatment to determine the efficiency of the treatment.
Tarcy U.S. Pat. No. 4,479,379 discloses a method and apparatus for continuous analysis of a gas and particulate stream. A sampling nozzle is placed in a gas and particulate stream and a solvent is injected creating an aerosol which enhances dissolution of gas in the solvent. A continuous analysis means examines the concentration of dissolved gas and particulate.
Also of interest are prior art Vaneldik U.S. Pat. No. 3,705,478 and Maatsck U.S. Pat. No. 3,457,787. The prior art patents show different means for measuring the concentration of particles in a gas and indeed in the environment of pollution control devices such as scrubbers and precipitators. None of the patents discloses the apparatus and method of the present invention.